·  Chapter 29 Menus

Program MenuDemo GUI

Objectives · To create menus (§29.2). ·  To learn the menu components JMenuBar, JMenu, JPopupMenu, JMenuItem, JCheckBoxMenuItem, and JRadioButtonMenuItem (§29.2). ·  To create popup menus (§29.3). · 

Menus Java provides several classes—JMenuBar, JMenu, JMenuItem, JCheckBoxMenuItem, and JRadioButtonMenuItem —to implement menus in a frame. A JFrame or JApplet can hold a menu bar to which the pull-down menus are attached. Menus consist of menu items that the user can select (or toggle on or off). Menu bars can be viewed as a structure to support menus.

The JMenuBar Class Step 1: JFrame f = new JFrame(); A menu bar holds menus; the menu bar can only be added to a frame. Following is the code to create and add a JMenuBar to a frame: Step 1: JFrame f = new JFrame(); f.setSize(300, 200); f.setVisible(true); JMenuBar mb = new JMenuBar(); f.setJMenuBar(mb);//attach a menu bar to a //frame

The JMenu Class Step 2: You attach menus onto a JMenuBar. The following code creates two menus, File and Help, and adds JMenu fileMenu = new JMenu("File", false); JMenu helpMenu = new JMenu("Help", true); mb.add(fileMenu); mb.add(helpMenu);

The JMenuItem Class Step3: You add menu items on a menu. The following code adds menu items and item separators in menu fileMenu: fileMenu.add(new JMenuItem("new")); fileMenu.add(new JMenuItem("open")); fileMenu.addSeparator(); fileMenu.add(new JMenuItem("print")); fileMenu.add(new JMenuItem("exit"));

Submenus Step 3.1:You can add submenus into menu items. The following code adds the submenus “Unix,” “NT,” and “Win95” into the menu item “Software.” JMenu softwareHelpSubMenu = new JMenu("Software"); JMenu hardwareHelpSubMenu = new JMenu("Hardware"); helpMenu.add(softwareHelpSubMenu); helpMenu.add(hardwareHelpSubMenu); softwareHelpSubMenu.add(new JMenuItem("Unix")); softwareHelpSubMenu.add(new JMenuItem("NT")); softwareHelpSubMenu.add(new JMenuItem("Win95"));

Check Box Menu Items Step 3.2 helpMenu.add(new JCheckBoxMenuItem("Check it"));

Radio Button Menu Items Step 3.3: JMenu colorHelpSubMenu = new JMenu("Color"); helpMenu.add(colorHelpSubMenu);   JRadioButtonMenuItem jrbmiBlue, jrbmiYellow, jrbmiRed; colorHelpSubMenu.add(jrbmiBlue = new JRadioButtonMenuItem("Blue")); colorHelpSubMenu.add(jrbmiYellow = new JRadioButtonMenuItem("Yellow")); colorHelpSubMenu.add(jrbmiRed = new JRadioButtonMenuItem("Red")); ButtonGroup btg = new ButtonGroup(); btg.add(jrbmiBlue); btg.add(jrbmiYellow); btg.add(jrbmiRed);

Radio Button Menu Items JMenu colorHelpSubMenu = new JMenu("Color"); helpMenu.add(colorHelpSubMenu);   JRadioButtonMenuItem jrbmiBlue, jrbmiYellow, jrbmiRed; colorHelpSubMenu.add(jrbmiBlue = new JRadioButtonMenuItem("Blue")); colorHelpSubMenu.add(jrbmiYellow = new JRadioButtonMenuItem("Yellow")); colorHelpSubMenu.add(jrbmiRed = new JRadioButtonMenuItem("Red")); ButtonGroup btg = new ButtonGroup(); btg.add(jrbmiBlue); btg.add(jrbmiYellow); btg.add(jrbmiRed);

29.2.2Image Icons, Keyboard Mnemonics, and Keyboard Accelerators JMenuItem jmiNew, jmiOpen; fileMenu.add(jmiNew = new JMenuItem("New")); fileMenu.add(jmiOpen = new JMenuItem("Open")); jmiNew.setIcon(new ImageIcon("image/new.gif")); jmiOpen.setIcon(new ImageIcon("image/open.gif")); helpMenu.setMnemonic('H'); fileMenu.setMnemonic('F'); jmiNew.setMnemonic('N'); jmiOpen.setMnemonic('O'); jmiOpen.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_O, ActionEvent.CTRL_MASK));

29.2.3 Example: Using Menus Objective: Create a user interface that performs arithmetic. The interface contains labels and text fields for Number 1, Number 2, and Result. The Result box displays the result of the arithmetic operation between Number 1 and Number 2.

Example: Using Menus Problem: Create a user interface that performs arithmetic. The interface contains labels and text fields for Number 1, Number 2, and Result. The Result box displays the result of the arithmetic operation between Number 1 and Number 2. MenuDemo Run